2005 Gas Gas TXT 125 Pro. Need help with air/fuel mixture and idle screw settings. And which screw is the fuel/air mixture?

[thesaint]

I have an 2005 Gas Gas TXT 125 Pro that i have been standing since 2017 without being started.

I tried to start the bike today but it would not start. 

The first thing i did was to check the for spark (which is okay) After that i took off the airfilter box and rear fender. 

I found an old hand pump spray bottle which i poored gasoline with 3% oil mixture in thinking of spraying fuel in to the carburettor. 

I am aware that it is supposed to be 2% but since the bike have not been started for a long time i decided to use 3% oil mixture.

So the first time i tried to start the bike i sprayed in 2 spray pumps with fuel from the the spray bottle. This was enough that the biked was about to start but stopped. 

On the second try i sprayed in 6 or 7 pumps of fuel using the spray bottle and the bike started really easy and ran for a little over 10 seconds before it stopped. 

I wonder if the settings both for the air/fuel mixture is wrong after i had the carburettor apart?

I hope that some here on the forum can help me with the standard settings for the fuel/air mixture and also the standard setting for the idle screw.  

I seem to remember that the air/fuel mixture is to screw the air/fuel mixture all the way in and the turn it back out about 1 and 1/2 turn back but i want to check that for sure so i hope some here on the forum can help me out.

 

When i use the hand pump and spray in about 7 pumps of fuel the bike runs great for about 10 seconds before it stops. So this is a fuel issue.  

 

Since i do not remember for sure which of the screws on the picture of the carburettor is the fuel/air mixture screw and which is the idle screw?  

 

See the picture below where i have marked what i think is the fuel/air screw with a yellow arrow and what i think is the idle screw with a red arrow. 

[konrad]

Your colored arrows are correct.   Dellorto PHBL 26 mixture screw is typically about 4 turns out from fully seated.

The pilot jet (and possibly starter jet too) is plugged from sitting for years with old premix.  Usually, spray carb cleaner is insufficient.  You need to clean the jet by passing a fine wire through the orifice.  But the diameter is critical, so I use pin gauges for that job.  Some people are uncomfortable using that method and should replace the jet(s) instead.

 

 

 

[thesaint]

I forgot to say that i took apart the carburetor some years ago and cleaned it. 

So this evening i took off the carburator to check it. Big was my suprise when i was to drain the float valve chamber and there was absolute no fuel at all in the float chamber. 

The float valve was stuck. So then i took the carburator to a friend of mine that is repairing motor bikes and he first loosened the float valve but he also said the spring on the float valve was sticking out to far.

So he tried to shorten it by re-fasten the 2 tiny small brass parts that hold the spring in the float valve but one of the small brass fasteners broke off so he took off the spring since it will work without the spring. 

After he fixed the float valve he checked the rest of the carburator. 

I guess the float valve was stuck because the carburator have been standing dry for a long time. Note that when i took the carburator apart a few years ago i managed to pull out the tip on the float valve, so i just put the tip back in the float valve and put the carburator back on the bike. But if i remember correct i did check if the float valve chamber had fuel it after i have had the carburator apart which it did. I guess that the fact that i pulled the tip of the float valve out can be the resason for this problem as well?

I guess it is not good to let the bike stand parked for a long time without any fuel in the carburetor or what do my fellow members here think about that? 

So when i came back home i put the carburator back on the bike, gave it a couple of sprays with fuel using the spray bottle and the bike started really easy and works runs great now 😊😊

Since it was late i just wanted to make sure the bike ran proper. The only work i had to do was to adjust the idle a little bit. 

I really hope the bike starts just as easy when i put the airbox with air filter back on the bike. Great if it starts as easy as it did today when i gave the carburator i couplle sprays with fuel 😊😊  

I will order a new float valve just in case. I need new anti freeze as well since i have not checked if there is enough or any coolant on the bike. I really do not feel for driving the engine to hot so i will change the anti freeze before use the bike.

Edited May 7 by thesaint
Forgot to write something

[lemur]

I think the problem is you don't realize how frequently the motorcycle carburetor needs service and once you start breaking parts inside there you are looking at replacement parts or a new carburetor.  No it won't matter if the carb is dry or full when you leave it sit because all of the fuel will evaporate out anyway since the float bowl is vented to the atmosphere.  There are no 'extra springs' in a carburetor that can be left out without impacting performance.  Running more oil in the fuel then called for will result in additional unburnt oil residue clogging up your exhaust system faster.

You can physically test a carburetor float bowl valve operation with only the float bowl removed, raise the float with your finger and watch the fuel flow or stop flowing when you lift the float with your finger, it operates on the same principal as a toilet.  Taking obvious safety precautions with fuel spill.

Idle adjust screw is always the one that pushes the throttle slide higher, low speed fuel or air adjustment screw will be the one 'not' located directly in the middle of the carburetor slide.  The adjustment you will likely need to visit most is not the screws which affect only low rev operation but rather the cir-clip position on the main jet needle which adjusts for lean to rich adjustment through 1/3rd to full throttle operation.  

 

[thesaint]

On 5/8/2024 at 3:18 PM, lemur said:

I think the problem is you don't realize how frequently the motorcycle carburetor needs service and once you start breaking parts inside there you are looking at replacement parts or a new carburetor.  No it won't matter if the carb is dry or full when you leave it sit because all of the fuel will evaporate out anyway since the float bowl is vented to the atmosphere.  There are no 'extra springs' in a carburetor that can be left out without impacting performance.  Running more oil in the fuel then called for will result in additional unburnt oil residue clogging up your exhaust system faster.

You can physically test a carburetor float bowl valve operation with only the float bowl removed, raise the float with your finger and watch the fuel flow or stop flowing when you lift the float with your finger, it operates on the same principal as a toilet.  Taking obvious safety precautions with fuel spill.

Idle adjust screw is always the one that pushes the throttle slide higher, low speed fuel or air adjustment screw will be the one 'not' located directly in the middle of the carburetor slide.  The adjustment you will likely need to visit most is not the screws which affect only low rev operation but rather the cir-clip position on the main jet needle which adjusts for lean to rich adjustment through 1/3rd to full throttle operation.  

 

Thanks a lot for helpful info 😊😊

I have to admit that i have not been working on motorbikes since i was a teenager. But i work a lot on sporty cars.

When you say the main jet needle do you mean the needle that is shown as part 36 on the parts list/drawing at the bottom here?

I did test the carburator flow valve by blowing in the fuel line and lifting the needle on the float valve so i knew the float valve was shut so there was no way the fuel could get in the float chamber. That was the first thing i did after i noticed the float chamber had no fuel at all. But before i took off the carburator i had already phoned a friend of mine that is a motorbike mechanic so i was on my way to him anyway. If i had fixed the float valve myself i would have freeded up the stuck float valve but i would not have noticed that the spring pushed the tip out to far as my friend noticed. But perhaps the float valve would have worked even if the tip on the float valve was sticcking out to far for all i know 😊 😊

I have off course ordered a new float valve to put in the carburator. Having said that the float valve that sit in my carburator with no spring is working perfect. Even if i park the bike without turning off the fuel tap the carburetor does not overflow.

Note that i always turn off the fuel tap but in this case i left the fuel tap open for a couple of hours just to check if the carburetor would overflow with the spring taken off the float valve.  

I am still saying that the float valve will work as it is supposed to without the spring. When there is enough fuel in the float chamber the float will rise and hit the needle on the float valve and the valve will shut off the fuel since the chamber is full. 

But i agree with you. There should be no parts left out in the carburetor or other parts on the bike. 

I had adjusted the fuel/air screw all the way in and turned it out back 1 and 1/2 turn but when the bike ran on idle i turned the fuel/air screw open close half a turn more. I was really lucky with the idle since it was almost perfect. 

As i said i was sure the bike would be hard to start after i had put the airbox with airfilter back was not the case at all 😊😊 The bike starts really easy 😊😊

From what i found out. When cold turn on the choke and the bike will star on the first or second try onthe kick starter. When warm just open up the throttle a little and it usually starts on the first try 😊😊

I have heard many replaces the Dellorto carburator with Kehin carburators but if you ask me the Dellorto carburetor on my bike sure is easy to start and runs great the little i have used the bike. 

About the 3% oil mixture is because i just thought it was better to use more oil since the bike have been standing since 2017. We are talking about 2 liters of fuel with a 3% oil mixture. When that is used up i will use 2% oil mixture in the fuel. 

I have always thought that on a 2 stroke it is better with to much oil than to little oil in the mixture. So i as said the 3% oil mixture was just to be on the safe side since the bike have been standing for so long. 

I would not have thought that the bike would be so easy to start. Especially when thinking of the short travel of the kick starter.

Thanks for all the help 😊😊 

 

 

 

Edited May 9 by thesaint

[thesaint]

On my TXT 125 Pro the protector rubber is not on the bike. I ordered the part some time ago so i have it on the shelf so i will put it on the bike.

I just put it on the bike where it is supposed to sit and to me it does not look to protect much i have to say. 

It is part 41/41A on the picture below. Also shown with a blue arrow. 

 

 

[thesaint]

On 5/7/2024 at 11:10 PM, konrad said:

Your colored arrows are correct.   Dellorto PHBL 26 mixture screw is typically about 4 turns out from fully seated.

The pilot jet (and possibly starter jet too) is plugged from sitting for years with old premix.  Usually, spray carb cleaner is insufficient.  You need to clean the jet by passing a fine wire through the orifice.  But the diameter is critical, so I use pin gauges for that job.  Some people are uncomfortable using that method and should replace the jet(s) instead.

 

 

 

I just noticed first now that you wrote that the mixture setting for the fuel/air screw is 4 turns out. Is that not much? Before i tried to start the bike i had the setting on 1 and 1/2 turn out and after i started the bike i opened the fuel/air screw a little more so on my bike it is almost 2 rounds out now. The bike runs great  but should i try to open up more? 

The pilot jet was and is open and in perfect order on my bike. 

I would not mind having the bike going slower so i do not know if i can tell if i put on a 9 tooth front sprocket front and 48 tooth rear sprocket? 

I think the front sprocket is a 8 tooth and the rear sprocket is a 42 tooth. Something tells me i will not notice any big difference with a a 9 tooth front sprocket front and 48 tooth rear sprocket

Edited May 11 by thesaint

[lemur]

"almost 2 rounds out" <- sounds much closer to a conventional carburetor setting 👍 if it works there leave it.  Pretty sure the low speed adjuster screw on a Dellorto controls fuel and on most other carbs it controls air so you might find adjustment alters the engine opposite to what you might expect.  I think as you turn the screw out you are enriching the fuel mixture on a Dellorto.  

What do they label part #27 & part # 30 on your diagram?  Those look more like the emulsion tube that I refer to as being most critical to clean after being subjected to fuel evaporation.  Variations on the name 'emulsion tube' are atomizer or pulverizer tube depending on the documentations original language.

[konrad]

12 hours ago, thesaint said:

I just noticed first now tha you wrote that the mixture setting for the fuel/air screw is 4 turns out. Is that not much? Before i tried to start the bike i had the setting on 1 and 1/2 turn out and after i started the bike i opened the fuel/air screw a little more so on my bike it is almost 2 riounds out now. The bike runs great  but should i try to open up more? 

 

 

The Dellorto is unlike a Japanese 2T carb (where 1.5 turn out is the normal starting point).   Despite being on the engine side of the slide, the Dellorto's mixture screw controls fuel (out is richer).   For the Dellorto, 3 to 4 turns out is typical.  If it runs best at 2 turns out, that's fine.

But don't be afraid to experiment with the mixture screw (just remember that the spring needs to be somewhat compressed to ensure the screw does not vibrate loose and fall out.) 

Most manufactures have a procedure for setting the mixture screw that optimizes idle smoothness or minimizes idle emissions.  I set the mixture screw for best performance just off idle.

Attached a pic for reference.  Mixture screws on the right left are for fuel, mixture screws on the left right are for air. 

 

 

Edited May 11 by konrad

[thesaint]

22 hours ago, lemur said:

"almost 2 rounds out" <- sounds much closer to a conventional carburetor setting 👍 if it works there leave it.  Pretty sure the low speed adjuster screw on a Dellorto controls fuel and on most other carbs it controls air so you might find adjustment alters the engine opposite to what you might expect.  I think as you turn the screw out you are enriching the fuel mixture on a Dellorto.  

What do they label part #27 & part # 30 on your diagram?  Those look more like the emulsion tube that I refer to as being most critical to clean after being subjected to fuel evaporation.  Variations on the name 'emulsion tube' are atomizer or pulverizer tube depending on the documentations original language.

According to the parts diagram part 27 is needle slow and part 28 is Jet slow 30.   

Below is a drwaing of the carburetor and the parts list 

When you open the drawing in a new window you can enlarge it and easy see the parts 

 

 

Edited May 11 by thesaint

[thesaint]

21 hours ago, konrad said:

 

The Dellorto is unlike a Japanese 2T carb (where 1.5 turn out is the normal starting point).   Despite being on the engine side of the slide, the Dellorto's mixture screw controls fuel (out is richer).   For the Dellorto, 3 to 4 turns out is typical.  If it runs best at 2 turns out, that's fine.

But don't be afraid to experiment with the mixture screw (just remember that the spring needs to be somewhat compressed to ensure the screw does not vibrate loose and fall out.) 

Most manufactures have a procedure for setting the mixture screw that optimizes idle smoothness or minimizes idle emissions.  I set the mixture screw for best performance just off idle.

Attached a pic for reference.  Mixture screws on the right left are for fuel, mixture screws on the left right are for air. 

 

 

Thanks for posting the picture and the help 😊😊 The fuel/air mixture screw i have on the bike is the one to the right without the spring (Screw number 3 from the left) 

The fuel/air mixture on my bike is turned out 2 turns as the bike is today (it runs great) But i will turn the out the fuel/air screw close to 2 more tuns out so it will be 4 turns out from fully closed and check how that works 😊 

You are absolute correct about screws can vibrate loose and fall off so i usually checks that. I have to say that when i check for loose screws i have never checked any adjustemnt screws on the carburator. 

Update! I have adjusted the fuel/air screw from fully in to a little over 3 turns out.

With the fuel/air screwed out a little over 3 turns compared to 2 rounds out it used to be i can not tell any difference of the mixtture settings.

When adjusted the fuel/air screw out 4 turns the screw feels a little to loose so for my liking. I think that there is a chance the fuel/air screw can vibrate loose.  

Anyway the bikes runs great with the fuel/air mixture screw adjusted out a little over 3 turns out from fully closed. The bike starts really easy both cold using the choke and warm with a little throttle with this mixture setting.  

 

 

Edited May 11 by thesaint

[lemur]

On 5/11/2024 at 11:52 AM, thesaint said:

According to the parts diagram part 27 is needle slow and part 28 is Jet slow 30.   

Below is a drwaing of the carburetor and the parts list 

When you open the drawing in a new window you can enlarge it and easy see the parts 

 

 

It says part #27 is the Emulsor for the needle jet.  That's the part that will need the most attention.

[thesaint]

14 hours ago, lemur said:

It says part #27 is the Emulsor for the needle jet.  That's the part that will need the most attention.

Thanks for letting me know 👍 👍 I was not aware of that. 

[lemur]

The job of the emulsion tube is to initiate the process of atomizing liquid fuel (and pre-mix lubricant) into the air intake stream, this is the part that makes your float level critical, the top half of the emulsion tube is to remain above the float bowl fuel level and the bottom half of that tube is submerged, emulsion tube is where air bubbles are introduced into the upward fuel flow, iIt will typically have a series of carefully placed tiny holes in the sides of a brass tube to introduce the air and those are the passages most likely to become plugged.  If the emulsion tube does not work you get raw fuel or no fuel getting dumped into the carburetor instead of a fine mist spray.  The whole assembly is similar to a fly sprayer or a perfume spray bottle or the nozzle on a can of spray paint fed by a toilet tank float valve.

[thesaint]

Jus back home from the post office after getting the new float valve/needle in the mail for my TXT Pro. 

When looking at the picture of the spring loaded needle i still think that if you take out/off the spring for the needle will not make any diffence at all since the needle will go up and shut off the fuel when the float chamber is full just as easy (if not more easy) without the spring.

The spring loaded needle sit on the carburetor just like it is shown on the picture so what the spring does is to push the needle down towards floats

You can see where i have tried to draw a yellow spring 

 

 

 

 

Edited May 18 by thesaint